Band engineering for efficient catalyst-substrate coupling for photoelectrochemical water splitting.

To achieve an overall efficient solar water splitting device, not only the efficiencies of photo-converter and catalyst are decisive, but also their appropriate coupling must be considered. In this report we explore the origin of a voltage loss occurring at the interface between a thin film amorphous silicon tandem cell and the TiO2 corrosion protection layer by means of XPS. We find that the overall device can be disassembled into its primary constituents and that they can be analyzed separately, giving insight into the device structure as a whole. Thus, a series of model experiments were conducted, each representing a part of the complete device. We finally arrive at the conclusion, that the formation of a SiO2 interfacial layer between the TiO2 protection layer and the silicon cell gives rise to the voltage loss observed for the whole device.

Photoelectrochemical and photovoltaic characteristics of amorphous-silicon-based tandem cells as photocathodes for water splitting.

In this study amorphous silicon tandem solar cells are successfully utilized as photoelectrodes in a photoelectrochemical cell for water electrolysis. The tandem cells are modified with various amounts of platinum and are combined with a ruthenium oxide counter electrode. In a two-electrode arrangement this system is capable of splitting water without external bias with a short-circuit current of 4.50 mA cm(-2). On the assumption that no faradaic losses occur, a solar-to-hydrogen efficiency of 5.54% is achieved. In order to identify the relevant loss processes, additional three-electrode measurements were performed for each involved half-cell.

Evaluating the effectiveness of a memory aid system.

BACKGROUND: The ability to remember future intentions is compromised in both healthy and cognitively impaired older adults. Assistive technology provides older adults with promising solutions to cope with this age-related problem. However, the effectiveness and efficiency of such systems as memory aids is seldom evaluated in controlled, randomized trials. OBJECTIVES: We evaluated the effectiveness of a memory aid system, the InBad (engl. InBath), for bathroom-related daily care. Conceptually, the InBad learns user behavior patterns and detects deviations from the learned pattern in order to notify the user of a forgotten task. METHODS: We simulated a challenging morning routine consisting of 22 bathroom activities with a sample of 60 healthy older adults. Participants were randomly assigned to three groups: (1) 'no memory support', i.e., participants received no support at all, (2) 'list support', i.e., participants could retrieve a list of all activities, and (3) 'system support', i.e., participants received prompts for specific activities that had not yet been executed. RESULTS: Both support groups executed significantly more activities compared to the 'no support' group. In addition, system support resulted in significantly better performance compared to list support with no significant differences between the two groups in overall task duration. CONCLUSION: The assistive support system was the most effective and efficient memory aid. The results suggest that assistive technology has the potential to enable older adults to remain safe and independent in their own home.

Solar hydrogen generation with wide-band-gap semiconductors: GaP(100) photoelectrodes and surface modification.

GaP, with its large band gap of 2.26 eV (indirect) and 2.78 eV (direct), is a very promising candidate for direct photoelectrochemical water splitting. Herein, p-GaP(100) is investigated as a photocathode for hydrogen generation. The samples are characterized after each preparation step regarding how their photoelectrochemical behavior is influenced by surface composition and structure using a combination of electrochemical and surface-science preparation and characterization techniques. The formation of an Ohmic back contact employing an annealed gold layer and the removal of the native oxides using various etchants are studied. It turns out that the latter has a pronounced effect on the surface composition and structure and therefore also on the electronic properties of the interface. The formation of a thin Ga(2)O(3) buffer layer on the p-GaP(100) surface does not lead to a clear improvement in the photoelectrochemical efficiency, neither do Pt nanocatalyst particles deposited on top of the buffer layer. This behavior can be understood by the electronic structure of these layers, which is not well suited for an efficient charge transfer from the absorber to the electrolyte. First experiments show that the efficiency can be considerably improved by employing a thin GaN layer as a buffer layer on top of the p-GaP(100) surface.

Nanostructured SnO2-ZnO heterojunction photocatalysts showing enhanced photocatalytic activity for the degradation of organic dyes.

Nanoporous SnO(2)-ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO(2) particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO(2) particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analyses, transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy. The SnO(2)-ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO(2) nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV-visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO(2)-ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO(2), that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO(2)-ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 ± 0.05 eV and 0.20 ± 0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO(2)-ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue than those of individual SnO(2) and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO(2)-ZnO photocatalyst because of the energy difference between the conduction band edges of SnO(2) and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO(2)-ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.

NADPH oxidases 1 and 4 mediate cellular senescence induced by resveratrol in human endothelial cells.

Resveratrol is believed to be partially responsible for the French paradox--the low risk of cardiovascular disease despite a high-fat diet in the French population. Recently, resveratrol has also been discussed as a life-span booster in several organisms. Age-related diseases are associated on the cellular level with senescence. We, therefore, hypothesized that resveratrol is vasoprotective by counteracting endothelial cell senescence. Surprisingly, we observed that chronic treatment with resveratrol (10 microM) was prosenescent in primary human endothelial cells. Resveratrol induced elevated reactive oxygen species (ROS) levels that were associated with and causally linked to an accumulation of cells in the S phase of the cell cycle, as measured by flow cytometry. We further show that cell accumulation in S phase leads to increased ROS and finally senescence. Using an siRNA approach, we clearly identified two NADPH oxidases, Nox1 and Nox4, as major targets of resveratrol and primary sources of ROS that act upstream of the observed S-phase accumulation.